Study on Overburden Structure and Mining Effect Characteristics of Super-thick and Hard Stratum
Supervisor:jiang jin quan
Super-thick and hard rock strata are distributed in many mining areas in China.Long-term suspension and instantaneous breakage of thick and hard strata are very easy to induce dynamic disasters such as face pressure,tremor,rock burst,surface subsidence and surface cracking,water and gas gushing in bed separation,which restrict the safe production of coal mines.It is of great theoretical significance and application value to study the law of breakage and migration,the structure of overburden rock,the law of development of overburden rock fissures,the law of mining stress and elastic energy change of coal and rock mass in the thick and hard rock strata,for realizing scientific mining under the thick and hard rock strata and preventing dynamic disasters.By means of in-situ measurement,physical simulation,mechanical simulation,numerical calculation and theoretical analysis,and by integrating the knowledge of rock mechanics,material mechanics,elasticity mechanics,soil mechanics,mining,mine pressure and strata control and other disciplines,a thorough and systematic study of the subject has been carried out.The main research contents and achievements are as follows:(1)Similar material simulation experiments show that with the advancing of the working face,the overlying strata are broken in groups with the key strata as the bottom supporting strata,and each group of strata is broken at different angles.The local fracture structures of overlying strata with different lithologic combinations are divided into lower soft-upper hard structure and lower hard-upper soft structure.Macroscopically,the "Ⅰ-Ⅱ double trapezoidal" structure is formed by the thick and hard stratum and the upper and lower weak strata.The mechanical model of key stratum rock beam breakage is constructed,the mechanical expression of key stratum breakage angle is deduced,and the influence law of key stratum thickness and overlying load layer thickness on key stratum breakage angle is obtained.On the basis of soil mechanics,the mechanical model of slip fracture of loose layer is established,and the mechanical expression of slip fracture angle of loose layer is deduced.A model of overlying strata structure and surface subsidence in stope with super-thick and hard stratum is established.(2)By means of mechanical simulation experiments,the development patterns of overburden failure under conditions of huge thick hard stratum and non-huge hard stratum in the overburden of stope are studied,and the special variation laws of overburden rock migration and separation development under the influence of huge thick hard strata are revealed.(3)Similar material simulation experiment was used to simulate the dynamic evolution process of overburden bed-seperation,revealing the influence of thick and hard stratum on the formation and development of overburden bed-seperation,and obtaining the distribution law of overburden water and gas evolution by bed-seperation.Based on the key stratum theory and the"S-R" instability theory,combined with the relationship between the limit span of overburden and the advancing distance of working face,a method to distinguish the "three zones" of overburden strata in stope is proposed,and the estimation methods of the separation range,the separation volume and the separation volume are put forward.(4)Similar material simulation experiment,mechanical simulation experiment and FLAC3D numerical simulation software were used to study the influence of the movement of thick and hard stratum on the change of stope stress and energy.Based on the load transfer characteristics of overburden structure and the ultimate bearing capacity of coal body,the calculation model of overburden structure load and abutment pressure is established,and the expression of the relationship between abutment pressure and main key stratum is obtained.The variation law of abutment pressure before and after the breaking of hard and thick main key stratum is quantitatively analyzed.(5)The method of coal seam mining and roof control under the influence of thick and hard stratum is optimized.Combining with the phenomena of gas blowout and surface subsidence in 10414 working face of Yangliu Coal Mine,the data of support pressure in 10416 working face and the case of microseismic activity in 10302 working face of Baodian Coal Mine,some conclusions are validated in engineering.